A method for preparing high-purity lithium bis(fluorosulfonyl)imide

Abstract

The present invention provides a method for preparing high-purity lithium bis(fluorosulfonyl)imide, belonging to the fields of chemical synthesis and lithium battery technology. Bis(chlorosulfonyl)imide is prepared by heating, stirring, and refluxing aminosulfonic acid, stirring thionyl chloride, and chlorosulfonic acid. The bis(chlorosulfonyl)imide is fluorinated and then concentrated and refined with a good solvent. After concentration to a certain concentration, a poor solvent is added for crystallization, and the crude bis(fluorosulfonyl)imide is filtered to obtain a salt. The crude product is then salified with alkaline lithium and slurried with dichloromethane solvent. The lithium bis(fluorosulfonyl)imide is filtered and dried to obtain the lithium bis(fluorosulfonyl)imide. The tourmaline ceramic balls prepared by the present invention are loaded with a thiazole / Sb complex and an organic lithium co-catalyst, which enhances the activity of the catalyst and, together with the metal chloride, improves the selectivity of the fluorination reaction and reduces the occurrence of side reactions.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical synthesis and lithium batteries, and particularly relates to a method for preparing high-purity lithium bis(fluorosulfonyl)imide. Background Art

[0002] Lithium bis(fluorosulfonyl)imide (LiFSI) is a promising alternative to lithium hexafluorophosphate (LFP) as a next-generation secondary lithium-ion battery electrolyte due to its high stability (no decomposition below 200°C), excellent low-temperature performance, good hydrolysis stability, and environmental friendliness. Lithium bis(fluorosulfonyl)imide can be used as an electrolyte additive in rechargeable lithium batteries, effectively reducing the low-temperature resistance of the SEI layer formed on the electrode plate surface at low temperatures and reducing the capacity loss of the lithium battery during storage, thereby improving battery capacity and electrochemical performance. It can also be used as an electrolyte for primary batteries, a polymerization catalyst, and an antistatic agent in industrial applications.

[0003] CN117069075A provides a method for preparing lithium bis(fluorosulfonyl)imide, comprising the following steps: providing an aqueous solution of lithium bis(fluorosulfonyl)imide, wherein the aqueous solution of lithium bis(fluorosulfonyl)imide contains an alkaline lithium salt; distilling and concentrating the aqueous solution of lithium bis(fluorosulfonyl)imide to obtain a lithium bis(fluorosulfonyl)imide aqueous concentrate; adding a non-aqueous organic solvent to the lithium bis(fluorosulfonyl)imide aqueous concentrate, mixing, and distilling to remove water to obtain an organic solution of lithium bis(fluorosulfonyl)imide.

[0004] CN116902930A discloses a method for preparing lithium bis(fluorosulfonyl)imide, comprising the following steps: S1, preparing sulfuryl fluoride; using calcium fluoride and sulfur trioxide as raw materials, reacting at high temperature in the presence of a catalyst to obtain a mixed gas containing sulfuryl fluoride; treating the mixed gas to obtain gaseous sulfuryl fluoride; S2, preparing lithium bis(fluorosulfonyl)imide; passing the gaseous sulfuryl fluoride obtained in step S1 into an organic solvent containing lithium nitride to obtain a slurry after reaction; performing solid-liquid separation on the slurry to obtain a first filtrate, concentrating the first filtrate and crystallizing to obtain a crystal slurry; and filtering the crystal slurry to obtain lithium bis(fluorosulfonyl)imide.

[0005] CN116835539A discloses a method for synthesizing high-purity lithium bis(fluorosulfonyl)imide by a step-by-step method. The present invention adopts the idea of ​​step-by-step reaction. In an environment filled with ammonia, sulfuryl fluoride is slowly introduced under the action of triethylamine to generate fluorosulfonamide triethylamine salt, which is then replaced with a strong acid to obtain fluorosulfonamide as an intermediate, and then continued to react with sulfuryl fluoride to obtain bis(fluorosulfonyl)imide triethylamine salt. In the lithiation process, potassium carbonate is first used to replace triethylamine to obtain KFSI, and then LiBF4 is used to react with KFSI to obtain LiFSI by double decomposition, which avoids the introduction of anionic impurities and provides conditions for the synthesis of high-purity lithium bis(fluorosulfonyl)imide.

[0006] CN116750733A discloses a method for preparing lithium bis(fluorosulfonyl)imide using sulfuryl fluoride. The method uses sulfuryl fluoride, ammonia, an organic base, a solvent, and lithium hydroxide to prepare lithium bis(fluorosulfonyl)imide. The method first performs preliminary purification by distillation and extraction, then performs filtration, and after adsorption on a perfluoropeptide-based molecular sieve, further removes trace impurity components in the crude product to obtain high-purity lithium bis(fluorosulfonyl)imide.

[0007] A major difficulty in the current application of LiFSI is the complex synthesis process conditions, and the synthesis process has relatively high requirements for equipment. The reaction is complex, the yield is low, the product purity is low, and the pollution is high, resulting in extremely high synthesis costs of LiFSI. Summary of the Invention

[0008] In view of this, the object of the present invention is to provide a method for preparing high-purity lithium bis(fluorosulfonyl)imide, which effectively improves the selectivity of the reaction, reduces side reactions, and significantly improves the purity of lithium bis(fluorosulfonyl)imide.

[0009] The technical solution adopted in the present invention is as follows:

[0010] A method for preparing high-purity lithium bis(fluorosulfonyl)imide comprises the following steps:

[0011] Step 1: Synthesis of bis(chlorosulfonyl)imide

[0012] Weigh 30-70 parts by mass of sulfamic acid into a round-bottom flask with a condenser reflux device, measure 90-210 parts of thionyl chloride and 36-84 parts of chlorosulfonic acid, stir and reflux at 100-120°C for 20-30 hours, absorb the overflowing gas with alkali solution, stop heating after the reaction mixture turns into a brown-yellow viscous liquid, continue stirring until the temperature in the oil bath pot drops to room temperature, and then perform reduced pressure vacuum distillation at a temperature of 100-120°C, and collect the fraction at 110-114°C to obtain bischlorosulfonyl imide.

[0013] Step 2: Fluorination of bis(chlorosulfonyl)imide to obtain bis(fluorosulfonyl)imide

[0014] A benign solvent is added to a tetrafluoroethylene reaction flask, followed by the dropwise addition of 600-700 parts of HClSI, 0.2-1 parts of a fluorination catalyst, and 0.02-0.1 parts of a co-catalyst. The temperature is raised to 30-100°C. While stirring, approximately 140-160 parts of anhydrous HF gas is slowly added dropwise, followed by the introduction of 400-600 parts of NH3. After 4-6 hours of reaction, a sample is taken for analysis. If the bis(chlorosulfonyl)imide content is ≤0.25%, the mixture is considered acceptable and proceeds to the next step. The fluoridation waste salt is filtered and dried to obtain a mixed waste salt of ammonium chloride and ammonium fluoride. This product is then concentrated and refined in the next step along with a benign solvent. After concentration to a certain concentration, a poor solvent is added for crystallization, and the crude bis(fluorosulfonyl)imide is filtered to obtain.

[0015] Step 3: Lithiation to salt

[0016] Add 500-600 parts of dichloromethane and 40-50 parts of basic lithium to a reaction flask, cool to 0-5°C, add 170-200 parts of bis(fluorosulfonyl)imide dropwise with stirring, stir for 1-3 hours, then raise the temperature to 20-25°C, add 300-400 parts of thionyl chloride dropwise, and stir for 10-20 hours. Filter, add 500-600 parts of dichloromethane and 0.05-0.3 parts of solvent to the filter cake, slurry, filter, and dry to obtain lithium bis(fluorosulfonyl)imide.

[0017] Furthermore, the alkali solution in step 1 is calcium hydroxide, cesium hydroxide, potassium hydroxide or sodium hydroxide.

[0018] Furthermore, the benign solvent in step 2 is one of acetonitrile, thionyl chloride, methyl carbonate, ethyl carbonate, and ethyl methyl carbonate.

[0019] Furthermore, the fluorination catalyst described in step 2 is one selected from SbCl5, TiCl4, SnCl4, and MoCl5.

[0020] Furthermore, the preparation method of the co-catalyst described in step 2 is:

[0021] 20-40 parts of acryloyl-containing tourmaline ceramic balls, 7-14 parts of organometallic complex, 0.001-0.02 parts of lithium acrylate, 3-7 parts of potassium tert-butoxide, and 200-300 parts of N-methylpyrrolidone are mixed and stirred at 60-70° C. for 100-180 minutes, filtered, and dried to obtain a co-catalyst.

[0022] Furthermore, the preparation method of the organometallic complex is:

[0023] Weigh 3-6 parts of dithiazole and 1-3 parts of SbC15, then add 80-100 parts of water, stir at 40-50°C for 100-160 minutes, remove water by vacuum distillation, dry, and let stand to cool naturally to room temperature to obtain an organometallic complex.

[0024] Furthermore, the preparation method of the acryl tourmaline ceramic ball is:

[0025] According to parts by mass, 100-140 parts of tourmaline ceramic balls are dissolved in 600-1000 parts of water, 3-6 parts of 3-methacryloxypropyltrimethoxysilane are added, and the mixture is stirred at 40-50° C. for 100-150 minutes, filtered, and dried to prepare tourmaline ceramic balls containing acryl groups.

[0026] Furthermore, the poor solvent in step 2 is one or more of dichloromethane, dichloroethane, chloroform, trichloroethane, carbon tetrachloride, n-hexane, cyclohexane, methanol, ethanol, trifluoroethanol, n-butanol, isopropanol or ether solvents.

[0027] Furthermore, the alkaline lithium described in step 3 is selected from any one of alkaline lithiums such as lithium alkoxide (such as lithium methanol, lithium ethoxide or lithium tert-butoxide), organic lithium carboxylate (such as lithium formate, lithium acetate, etc.), lithium oxide, lithium hydroxide, lithium carbonate, etc.

[0028] Furthermore, the drying in step three is vacuum drying; the drying temperature is 40-50° C., and the drying time is 6-10 hours.

[0029] Furthermore, the solvent in step three is a crown ether, specifically one or more of 18-crown-6, 15-crown-5, and 12-crown-4.

[0030] Reaction mechanism

[0031] The reaction mechanism of synthesizing bischlorosulfonyl imide in step 1 is:

[0032] NH2SO3H+2SOCl2+ClSO3H→HN(SO2Cl)2+2SO2↑+3HCl↑

[0033] The reaction mechanism of fluorination of bis(chlorosulfonyl)imide to bis(fluorosulfonyl)imide in step 2 is as follows:

[0034] HN(SO2Cl)2+2HF→HN(SO2F)2+2HCl↑

[0035] The reaction mechanism of lithiation to salt in step 3 is:

[0036]

[0037] Reaction mechanism of co-catalyst:

[0038] A mercapto addition reaction occurs between tourmaline ceramic balls containing acryloyl groups, an organic metal complex, and lithium acrylate to obtain a tourmaline ceramic ball-loaded thiazole / Sb complex; the organic lithium co-catalyst and the chloride metal together catalyze the fluorination reaction to improve the selectivity and reduce side reactions.

[0039] Technical Effects

[0040] Tourmaline ceramic balls support a thiazole / Sb complex, acting as an organolithium cocatalyst. Together with metal chlorides, they enhance the selectivity of fluorination reactions. Thiazole and its complex with Sb act as cocatalysts in this reaction, enabling organofluorination reactions to proceed at lower temperatures, improving product selectivity and minimizing side reactions. The organolithium compound interacts with the thiazole complex, enhancing catalyst activity and increasing reaction rate. This results in improved selectivity and reduced side reactions. Specific embodiments

[0041] The invention will be further described below by means of specific embodiments:

[0042] 1. Purity: Purity of lithium bis(fluorosulfonyl)imide = mass of lithium bis(fluorosulfonyl)imide in the mixture / mass of the mixture × 100%;

[0043] 2. Yield: Yield of lithium bis(fluorosulfonyl)imide = actual amount of lithium bis(fluorosulfonyl)imide produced / theoretical amount of lithium bis(fluorosulfonyl)imide produced × 100%.

[0044] Example 1

[0045] Step 1: Synthesis of bis(chlorosulfonyl)imide

[0046] Weigh 30 g of aminosulfonic acid into a round-bottom flask with a condenser reflux device, measure 90 g of dichlorothionyl and 36 g of chlorosulfonic acid, stir and reflux at 100 ° C for 20 hours, absorb the overflowing gas with calcium hydroxide, stop heating when the reaction mixture turns into a brown viscous liquid, continue stirring until the temperature in the oil bath pot drops to room temperature, and then perform vacuum distillation at a temperature of 100 ° C. Collect the fraction at 110 ° C to obtain bischlorosulfonyl imide.

[0047] Step 2: Fluorination of bis(chlorosulfonyl)imide to obtain bis(fluorosulfonyl)imide

[0048] Add acetonitrile to a tetrafluoroethylene reaction flask, dropwise add 600g of HClSI, 0.2g of SbCl5 catalyst, and 0.02g of co-catalyst. Raise the temperature to 300°C, slowly add approximately 140g of anhydrous HF gas dropwise with stirring, and introduce 400g of NH3. After 4 hours of reaction, sample analysis reveals a bis(chlorosulfonyl)imide content of ≤0.25%, which is considered acceptable and proceeds to the next step. The fluorinated waste salt is filtered and dried to obtain a mixed waste salt of ammonium chloride and ammonium fluoride. This product, along with acetonitrile, proceeds to the next step of concentration and refining. After concentration to a certain concentration, dichloromethane is added for crystallization, and the crude bis(fluorosulfonyl)imide is obtained by filtration.

[0049] Step 3: Lithiation to salt

[0050] Add 500g of dichloromethane and 40g of lithium methoxide to the reaction flask, cool to 0°C, and add 170g of bis(fluorosulfonyl)imide dropwise with stirring. Stir for 1 hour, then raise the temperature to 20°C and add 300g of thionyl chloride dropwise. Stir for 10 hours. Filter, add 500g of dichloromethane and 0.05g of 18-crown-6 to the filter cake, slurry, filter, and dry to obtain lithium bis(fluorosulfonyl)imide.

[0051] The preparation method of the co-catalyst described in step 2 is:

[0052] 20 g of acryloyl-containing tourmaline ceramic balls, 7 g of an organic metal complex, 0.001 g of lithium acrylate, 3 g of potassium tert-butoxide, and 200 g of N-methylpyrrolidone were mixed and stirred at 60° C. for 100 minutes, filtered, and dried to obtain a co-catalyst.

[0053] The preparation method of the organometallic complex is:

[0054] Weigh 3g of dithiazole and 1g of SbCl5, add 80g of water, stir at 40℃ for 100 minutes, remove water by vacuum distillation, dry, and let stand to cool naturally to room temperature to obtain an organometallic complex.

[0055] The preparation method of the acryl tourmaline ceramic ball is:

[0056] 100 g of tourmaline ceramic balls were dissolved in 600 g of water, 3 g of 3-methacryloxypropyltrimethoxysilane was added, and the mixture was stirred at 40° C. for 100 minutes, filtered, and dried to obtain tourmaline ceramic balls containing acryl groups.

[0057] The drying in step 3 is vacuum drying; the drying temperature is 40° C., and the drying time is 6 h.

[0058] Example 2

[0059] Step 1: Synthesis of bis(chlorosulfonyl)imide

[0060] Weigh 50 g of aminosulfonic acid into a round-bottom flask with a condenser reflux device, measure 150 g of dichlorothionyl and 60 g of chlorosulfonic acid, stir and reflux at 110 ° C for 25 hours, absorb the overflowing gas with potassium hydroxide, stop heating when the reaction mixture becomes a brown viscous liquid, continue stirring until the temperature in the oil bath pot drops to room temperature, and then perform vacuum distillation at a temperature of 110 ° C. Collect the fraction at 112 ° C to obtain bischlorosulfonyl imide.

[0061] Step 2: Fluorination of bis(chlorosulfonyl)imide to obtain bis(fluorosulfonyl)imide

[0062] Add thionyl chloride to a tetrafluoroethylene reaction flask, then dropwise add 650g of HClSI, 0.6g of TiCl4 catalyst, and 0.06g of a co-catalyst. Raise the temperature to 65°C, slowly add approximately 150g of anhydrous HF gas dropwise with stirring, and introduce 500g of NH3. After 5 hours of reaction, sample analysis reveals a bis(chlorosulfonyl)imide content of ≤0.25%, which is considered acceptable and proceeds to the next step. The fluorinated waste salt is filtered and dried to obtain a mixed waste salt of ammonium chloride and ammonium fluoride. This product, along with the thionyl chloride, proceeds to the next step of concentration and refining. After concentration to a certain concentration, dichloroethane is added for crystallization, and filtration yields the crude bis(fluorosulfonyl)imide.

[0063] Step 3: Lithiation to salt

[0064] Add 550g of dichloromethane and 45g of lithium hydroxide to the reaction flask, cool to 3°C, and add 185g of bis(fluorosulfonyl)imide dropwise with stirring. Stir for 2h, then raise the temperature to 23°C and add 350g of thionyl chloride dropwise. Stir for 15h. Filter, add 550g of dichloromethane and 0.2g of 15-crown ether-5 to the filter cake, slurry, filter, and dry to obtain lithium bis(fluorosulfonyl)imide.

[0065] The preparation method of the co-catalyst described in step 2 is:

[0066] 30 g of acryloyl-containing tourmaline ceramic balls, 11 g of an organic metal complex, 0.01 g of lithium acrylate, 5 g of potassium tert-butoxide, and 250 g of N-methylpyrrolidone were mixed and stirred at 65° C. for 140 minutes, filtered, and dried to obtain a co-catalyst.

[0067] The preparation method of the organometallic complex is:

[0068] Weigh 4.5 g of dithiazole and 2 g of SbCl5, add 90 g of water, stir at 45 ° C for 130 minutes, remove water by vacuum distillation, dry, and let stand to cool naturally to room temperature to obtain an organometallic complex.

[0069] The preparation method of the acryl tourmaline ceramic ball is:

[0070] 120 g of tourmaline ceramic balls were dissolved in 800 g of water, 4.5 g of 3-methacryloyloxypropyltrimethoxysilane was added, and the mixture was stirred at 45° C. for 125 minutes, filtered, and dried to obtain tourmaline ceramic balls containing acryl groups.

[0071] The drying in step 3 is vacuum drying; the drying temperature is 45° C., and the drying time is 8 h.

[0072] Example 3

[0073] Step 1: Synthesis of bis(chlorosulfonyl)imide

[0074] Weigh 70 g of aminosulfonic acid into a round-bottom flask with a condenser reflux apparatus, measure 210 g of dichlorothionyl and 84 g of chlorosulfonic acid, stir and reflux at 120 ° C for 30 hours, absorb the overflowing gas with sodium hydroxide solution, stop heating after the reaction mixture turns into a brown viscous liquid, continue stirring until the temperature in the oil bath pot drops to room temperature, and then perform vacuum distillation at a temperature of 120 ° C. Collect the fraction at 114 ° C to obtain bischlorosulfonyl imide.

[0075] Step 2: Fluorination of bis(chlorosulfonyl)imide to obtain bis(fluorosulfonyl)imide

[0076] Add ethyl carbonate to a tetrafluoroethylene reaction flask, then dropwise add 700g of HClSI, 1g of SnCl4 catalyst, and 0.1g of a co-catalyst. Raise the temperature to 100°C, slowly add approximately 160g of anhydrous HF gas dropwise with stirring, and introduce 600g of NH3. After 6 hours of reaction, sample analysis reveals a bis(chlorosulfonyl)imide content of ≤0.25%, which is considered acceptable and proceeds to the next step. The fluorinated waste salt is filtered and dried to yield a mixed waste salt of ammonium chloride and ammonium fluoride. This product, along with good ethyl carbonate, proceeds to the next step of concentration and refining. After concentration to a certain concentration, trifluoroethanol is added for crystallization, and the crude bis(fluorosulfonyl)imide is filtered to obtain.

[0077] Step 3: Lithiation to salt

[0078] Add 600g of dichloromethane and 50g of basic lithium to the reaction flask, cool to 5°C, and add 200g of bis(fluorosulfonyl)imide dropwise with stirring. Stir for 3h. Then, raise the temperature to 25°C and add 400g of thionyl chloride dropwise. Stir for 20h. Filter, add 600g of dichloromethane and 0.3g of 12-crown ether-4 to the filter cake, slurry, filter, and dry to obtain lithium bis(fluorosulfonyl)imide.

[0079] The preparation method of the co-catalyst described in step 2 is:

[0080] 40 g of acryloyl-containing tourmaline ceramic balls, 14 g of an organic metal complex, 0.02 g of lithium acrylate, 7 g of potassium tert-butoxide, and 300 g of N-methylpyrrolidone were mixed and stirred at 70° C. for 180 minutes, filtered, and dried to obtain a co-catalyst.

[0081] The preparation method of the organometallic complex is:

[0082] Weigh 6 g of dithiazole and 3 g of SbCl5, add 100 g of water, stir at 50 ° C for 160 minutes, remove water by vacuum distillation, dry, and let stand to cool naturally to room temperature to obtain an organometallic complex.

[0083] The preparation method of the acryl tourmaline ceramic ball is:

[0084] 140 g of tourmaline ceramic balls were dissolved in 1000 g of water, 6 g of 3-methacryloxypropyltrimethoxysilane was added, and the mixture was stirred at 50° C. for 150 minutes, filtered, and dried to obtain tourmaline ceramic balls containing acryl groups.

[0085] The drying in step 3 is vacuum drying; the drying temperature is 50° C., and the drying time is 10 h.

[0086] Comparative Example 1

[0087] No co-catalyst is added in step 2, and the rest of the technical scheme is the same as in Example 1.

[0088] Comparative Example 2

[0089] No acryl tourmaline ceramic balls were added to the co-catalyst, and the rest of the technical solutions were the same as in Example 1.

[0090] Comparative Example 3

[0091] No organometallic complex is added to the co-catalyst, and the rest of the technical scheme is the same as in Example 1.

[0092] Comparative Example 4

[0093] No lithium acrylate is added to the co-catalyst, and the rest of the technical scheme is the same as that of Example 1.

[0094] Table 1 shows the purity and yield of the target products of Examples 1-3 and Comparative Examples 1-4.

[0095] purity / % Yield / % Example 1 99.94 93.74 Example 2 99.97 94.53 Example 3 99.99 95.97 Comparative Example 1 82.12 80.77 Comparative Example 2 88.35 84.89 Comparative Example 3 91.53 87.39 Comparative Example 4 93.35 90.35

[0096] It can be seen from the above table that compared with the comparative example, the yield and purity of the bisfluorosulfonyl imide prepared in the example are higher.

[0097] The embodiments described above only express several implementation methods of the present application, which are convenient for understanding the technical solutions of the present application in a specific and detailed manner, but they cannot be understood as limiting the scope of protection of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all fall within the scope of protection of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the scope of protection of the claims attached to the present application. Therefore, the scope of protection of the patent of this application shall be based on the content of the attached claims, and the description can be used to interpret the content of the claims.

Claims

1. A method for preparing high-purity lithium bis(fluorosulfonyl)imide, characterized in that: The steps include: Step 1: Synthesis of bis(chlorosulfonyl)imide Weigh 30-70 parts by mass of aminosulfonic acid into a round-bottom flask with a condenser reflux apparatus, add 90-210 parts of thionyl chloride and 36-84 parts of chlorosulfonic acid, stir and reflux at 100-120°C for 20-30 hours, absorb the overflowing gas with alkali solution, stop heating after the reaction mixture turns into a brown-yellow viscous liquid, continue stirring until the temperature in the oil bath drops to room temperature, and then perform vacuum distillation at a temperature of 100-120°C. Collect the fraction at 110-114°C to obtain bischlorosulfonyl imide; Step 2: Fluorination of bis(chlorosulfonyl)imide to obtain bis(fluorosulfonyl)imide A benign solvent is added to a tetrafluoroethylene reaction flask, and 600-700 parts of HClSI, 0.2-1 parts of a fluorination catalyst, and 0.02-0.1 parts of a co-catalyst are added dropwise. The temperature is raised to 30-100°C, and 140-160 parts of anhydrous HF gas is slowly added dropwise with stirring, and 400-600 parts of NH3 are introduced. After reacting for 4-6 hours, a sample is taken for analysis, and if the bis(chlorosulfonyl)imide content is ≤0.25%, it is considered qualified and transferred to the next step; the fluorinated waste salt is filtered and dried to obtain a mixed waste salt of ammonium chloride and ammonium fluoride. The product is then concentrated and refined in the next step with a benign solvent. After concentration to a certain concentration, a poor solvent is added for crystallization, and the crude bis(fluorosulfonyl)imide is obtained by filtration; Step 3: Lithiation to salt Add 500-600 parts of dichloromethane and 40-50 parts of basic lithium to the reaction flask, cool to 0-5°C, add 170-200 parts of bis(fluorosulfonyl)imide dropwise with stirring, stir for 1-3 hours, then raise the temperature to 20-25°C, add 300-400 parts of thionyl chloride dropwise, stir for 10-20 hours, filter, add 500-600 parts of dichloromethane and 0.05-0.3 parts of solvent to the filter cake, beat the mixture, filter, and dry to obtain lithium bis(fluorosulfonyl)imide; The preparation method of the co-catalyst described in step 2 is: 20-40 parts of acryloyl-containing tourmaline ceramic balls, 7-14 parts of an organic metal complex, 0.001-0.02 parts of lithium acrylate, 3-7 parts of potassium tert-butoxide, and 200-300 parts of N-methylpyrrolidone are mixed and stirred at 60-70° C. for 100-180 minutes, filtered, and dried to obtain a co-catalyst; The preparation method of the organometallic complex is: Weigh 3-6 parts of dithiazole and 1-3 parts of SbCl5, add 80-100 parts of water, mix and stir at 40-50°C for 100-160 minutes, remove water by vacuum distillation, dry, and let stand to cool naturally to room temperature to obtain an organometallic complex.

2. The method for preparing high-purity lithium bis(fluorosulfonyl)imide according to claim 1, wherein: The alkali solution in step 1 is calcium hydroxide, cesium hydroxide, potassium hydroxide or sodium hydroxide.

3. The method for preparing high-purity lithium bis(fluorosulfonyl)imide according to claim 1, wherein: The benign solvent described in step 2 is one of acetonitrile, thionyl chloride, methyl carbonate, ethyl carbonate, and ethyl methyl carbonate.

4. The method for preparing high-purity lithium bis(fluorosulfonyl)imide according to claim 1, wherein: The fluorination catalyst described in step 2 is one selected from SbCl5, TiCl4, SnCl4, and MoCl5.

5. The method for preparing high-purity lithium bis(fluorosulfonyl)imide according to claim 1, wherein: The preparation method of the acryl tourmaline ceramic ball is as follows: According to parts by mass, 100-140 parts of tourmaline ceramic balls are dissolved in 600-1000 parts of water, 3-6 parts of 3-methacryloxypropyltrimethoxysilane are added, and the mixture is stirred at 40-50° C. for 100-150 minutes, filtered, and dried to prepare tourmaline ceramic balls containing acryl groups.

6. The method for preparing high-purity lithium bis(fluorosulfonyl)imide according to claim 1, wherein: The poor solvent in step 2 is one or more of dichloromethane, dichloroethane, chloroform, trichloroethane, carbon tetrachloride, n-hexane, cyclohexane, methanol, ethanol, trifluoroethanol, n-butanol, isopropanol or ether solvents.

7. The method for preparing high-purity lithium bis(fluorosulfonyl)imide according to claim 1, wherein: The alkaline lithium described in step 3 is selected from any one of lithium methoxide, lithium ethoxide, lithium tert-butoxide, lithium formate, lithium acetate, lithium oxide, lithium hydroxide, and lithium carbonate.

8. The method for preparing high-purity lithium bis(fluorosulfonyl)imide according to claim 1, wherein: The drying in step three is vacuum drying; the drying temperature is 40-50° C., and the drying time is 6-10 hours; and the solvent is one or more of 18-crown-6, 15-crown-5, and 12-crown-4.

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